Combustor for fluid fuels



March 14, 1961 R. B. SCHIEFER 2,974,485

COMBUSTOR FOR FLUID FUELS Filed June 2, 1958 Invenror- Richard BSChiefer2,974,485 COMBUSTOR FOR FLUID FUELS Richard B. Schiefer, Schenectady,N.Y., assignor to General Electric Company, a corporation of New YorkFiled June 2, 1958, Ser. No. 739,411

4 Claims. (Cl; 60--39.6'5)

This invention relates to combustion apparatus, particularly to animproved combustor for fluid fuels as may be used in gas turbinepowerplants, rocket engines, jet engines for aircraft, and similarapparatus.

Difficulty has been encountered in applying the socalled Nerad typecombustor, described in United States Patent 2,601,000, issued June 17,1952 and assigned to the same assignee as the present application, tothe burning of heavy residual fuel oils, such as those known to thetrade as Bunker C. These are extremely viscous hydrocarbons, so thick asto be solid at temperatures below about 30 F. Because of the low cost,it is of substantial economic importance to the gas turbine user to beable to burn such fuel. Special air-atomizing type nozzles have beendeveloped for this purpose, one of which is shown in the patent toNeugebauer et al.-2,801,134, issued July 30, 1957 and assigned to thesame assignee as the present application.

Specifically, certain Nerad type combustors, equipped with anair-atomizing nozzle of the type described for burning Bunker C oils,have been found to produce quantities of smoke which would render a gasturbine powerplant unacceptable in railway locomotive service, or instationary plants in residential areas. The incomplete combustion ofcourse may increase troubles due to carbon deposition in the combustionchamber and on the stationary nozzles of the turbine, in the bucketpassages, etc.

In studying this smoke problem, I conceived the basic difficulty to tobe that the Nerad combustor introduces too much cold air into thefuel-air mixing and primary combustion zone, this large flow into theclosed end of the combustion space being necessary in order to establishthe strong central reverse flow toward the fuel nozzle, so as to createthe double opposed vortex flow referred to as the tore in theabove-mentioned Nerad patent. Because of the difliculty of getting theheavy' residual fuel particles to mix with the combustion air and beginburning, it is particularly important to have a strong tore formed inthe primary combustion zone. In troducing more air for this purpose inthe manner of the Nerad invention increases the problems due to unburnedfuel particles resulting from burning particles being quenched by thestrong tore-forming air jets.

The problem is still further complicated by the fact that thesignificant quantity of air employed in the air atomizing type fuelnozzle to spray the heavy residual fuel oil produces high axial velocitycomponents down the central core of the combustion space, whichvelocities are in opposition to the reverse circulation which the jetsof combustion air are intended to create. Thus, the air-atomizing nozzleproduces a spray which tends to oppose the basic flow pattern requiredin the primary mixing and ignition zone for successful operation of theNerad combustor.

I have foundthat in trying the use an air-atomizing type nozzle forresidual fuels in a conventional Nerad combustor, an over-rich fuel-airmixture tends to accu- 23%,485 Patented Mar. 14, 1961 mulate in theclosed or dome end of the combustion space. Particles of unburned orpartly burned fuel from this zone tend to migrate along the side wallsof the combustion chamber liner, apparently carried by the film ofcooling air which is ordinarily provided in the Ne'rad combustor toshield the cool metal surfaces from' fuel'nozzle to produce .a strongtoroidal circulation to insure effective ignition and completecombustion, the flow of combustion air into the primary zone beingarranged to avoid quenching of the burning fuel particles.

A further object is to provide an improved fuel-air mixing arrangementfor a fiuid fuel combustor in which the primary combustion flow patterncompletely fills the closed end of the combustion space, so as to effecta larger ignition zone, higher temperatures in the primary combustionzone, and lower through-flow velocities, so the fuel particles tend toremain for a longer time in the primary mixing and ignition zone. 7

Another object is to provide a combustor of the type described in whichthe flow into the closed end of the combustion space which comprises theprimary mixing and ignition air is more definitely separated from theside-wall air jets which provide the secondary combustion air andthecooling and dilution air flow, so that the flow for each may be moreclearly determined and the respective quantities and velocities bettercontrolled.

Other objects and advantages will become apparent from the followingdescription taken in connection'with the accompanying drawings, in whichFig. 1 is a longitudinal sectional View of a fiuid fuel combustor inaccordance with the invention;

Fig. 2 is a longitudinal section of a modified combustor;

Fig. 3 is an end view of the end dome of Fig. 2, taken on the plane 3-3;and

Fig. 4 is a partial sectional view of a detailed modification of the enddome of Fig. 2.

Generally stated, the inventionis practiced by providing a combustor enddome structure having nozzle means for injecting a precisely controlledamount of air, both to supply the quantity of oxygen required for bestignition characteristics and to set up a predetermined flow patternwhich will cooperate with the jet from the fuel nozzle to produce astrong reverse flow or toroidal recirculation completely filling theprimary mixing Zone, to insure a longer time of retention of the fuelparticles in the mixing and ignition zone, the secondary air inlets inthe side wall of the combustor liner being of carefully coordinated sizeand location so as to furnish just the right quantity of additional airrequired to carry out the combustion process effectively, withouttending to quench the burning fuel particles or disrupt the toroidalflow in the mixing zone. 7

Referring now more specifically to the drawings, it will be seen thatthe invention is illustrated as applied to a gas turbine combustorcomprising an outer housing identified generally at 1 defining an airinlet passage la and having a cylindrical portion 1b surrounding andspaced from a cylindrical liner 2 which forms the side walls of thecombustion space 3. It will be apparent that the annular passage 1cforms a cooling and air supply passage surrounding the liner 2. Theinlet or closed end of the combustion space is defined by an end dome orclosure identified 4. The fuel is injected by a suitable fuel 3 spraynozzle 5, which may be of the type described by the above-identifiedNeugebauer et al. Patent 2,801,134 when the fuel is a heavy residualtype oil.

While such mechanical details are not necessary to an understanding ofthe present invention, the liner is shown as supported from thecylindrical outer. housing 1b by a plurality of radially extendingdowels or struts 6a. Similarly, the end dome 4 is supported by radialdowels or struts 6b, while the central portion of the end dome defines areinforcing ring 4a having a central opening fitting the end portion aof the fuel nozzle 5.

The fuel nozzle 5 is of a type adapted to project a fuel-air spraypattern in the form of a solid, rather than hollow, conical spraypattern, shown at 7. a It is significant to note that the vertex angleof this spraypattern is shown in Fig. 1 as being on the order of 20, butmay be up to a maximum of about 60. It is important to note that thefuel nozzle 5 is of a type which employs air or other auxiliary fluid asan atomizing agent to break up the viscous fuel oil into a fine spray,and that the quantity of this auxiliary fluid and the vertex angle ofthe spray pattern is such that the fuel pattern '7 has very high axialvelocity components, the importance of which will be noted moreparticularly hereinafter. As in the Nerad type combustor, the end dome 4and the extreme upstream end of the cylindrical liner 2 cooperate todefine a primary mixing and ignition zone, while the succeedingdownstream portions of the liner 2 define the secondary combustion zoneand a cooling and dilution zone. The location and extent of theserespective combustion zones will be noted later.'

In accordance with the present invention, the end closure member 4 andthe extreme upstream end portion of the liner 2 define a plurality ofjet-forming means for injecting the primary mixing and ignition air intothe combustion space in carefully controlled amounts and directions soas to produce the characteristic double opposed toroidal flow path orsmoke ring vortex represented by the arrows 8 in Fig. 1. The formationof this smoke ring vortex or tore goes to the very essence of thepresent invention; and it will be seen that the direction of rotation ofthis tore is in the reverse direction as compared with the tore of theNerad combustor of Patent The primary air inlet nozzle means comprise anannular nozzle identified generally at .9, radial jet-forming nozzlemeans 10, and generally axial jet-forming means 11. The secondaryair-admitting nozzle means comprise a plurality of rows ofcircumferentially spaced ports identified 12, 13, and 14.

Referring now more specifically to the primary jetforming means, theannular nozzle 9 is formed by an inwardly and axially projecting portionformed integral with or secured to the extreme upstream end of liner 2.This liner upstream end portion is supported in carefully spacedrelation to the downstream end of the dome 4 by the support means 6a, 6bso as to define a uniform annular nozzle identified 9a. It will be seenthat this nozzle directs a strong annular jet of fluid in an upstreamdirection as indicated by arrows 9b. This annular jet tends to flowupstream and radially inwardly along the inner surface of the dome 4. Itis to be particularly noted that this annular jet 9b is generallytangential to, and in the same direction as, the toroidal flow path 8.

The radial jet-producing nozzles 10 comprise a circumferential row ofports having curved vanes designated 10a, 10b. These vanes may besupported from the end dome by a plate member identified 100. This maybe a single support plate disposed across the middle of the air inletopening in dome 4, or the opening may be square or rectangilar in shape,with an end plate 100 at either side of the opening. Other mechanicalarrangements will be obvious to those skilled in the art, and it is tobe understood that the structure shown in Fig. 1 is merelyrepresentative of any suitable nozzle means for producing strong jetshaving a discharge velocity component generally radial to the axis ofthe liner 2, these radial jets being identified by the arrows 10d. Hereagain it will be observed that these radial jets are generallytangential to, and in the same direction as, the toroidal flow 8.

The third primary jet-forming means associated with the end dome 4comprise the circumferential row of flaring inlet nozzles identified 11.It will be seen that these project jets identified by the arrows 11a ina generally axial direction and tangent also to the toroidal flow path8. Flaring inlet nozzles of this type are described more specifically inthe patent to K. D. McMahan, No. 2,510,645, issued June 6, 1950, andassigned to the same assignee as the present application.

It will of course be understood that other mechanical structures may beemployed for the three different types of primary jet-forming nozzlesshown in Fig. 1. For instance, the annular nozzle 9a could be formed bystructure such as that shown in the patent to Garber 2,555,965, issuedJune 5, 1951, or in the patent to Blatz-- 2,581,999, issued January 8,1952, both assigned to the same assignee as the present application.Also, the vanetype nozzle 10 could be replaced by the flaring inlet typenozzle 11. Or, the nozzle 11 might be replaced by a simple circular holein the end dome, as noted more particularly in connection with Fig. 2.

It will be seen that the important criterion is that all the jet-formingmeans associated with the initial mixing and ignition zone are of typescapable of injecting strong jets of air in precisely controlledquantities and with a carefully controlled direction so that all suchjets are generally tangent to the desired toroidal flow path 8. It willbe obvious from Fig. 1 that the jets 9b, 10d, and 11a will cooperate toproduce a strong reverse circulation represented *by the tore 8. Thecreation of such a strong and stable tore is particularly important in acombustor burning viscous residual fuels like Bunker C oil. This toreinsures retention of the fuel particles in the primary mixing andignition zone for a sufficient length of time to bring them to ignitiontemperature and into contact with oxygen and hot gases adequate toeffect ignition and initial combustion of the fuel particle. Failure toso retain the fuel particle in this initial mixing zone for a suificientperiod of time is a prime cause of incomplete combustion and smoke. Thistoroidal flow path is also of great importance with respect to theproblem of blow-out, which becomes particularly important at low load.With the primary air jet-forming means disclosed herein, a strong stabletore 8 is formed and maintained over the complete range of operationfrom maximum capacity down to flow rates on the order of 5% of themaximum fuel flow rate.

It is important to note in Fig. 1 that the kinetic energy of the fuelparticles and the air or other fluid employed in nozzle 5 to effectatomization of the fuel oil has, by reason of the high axial velocitycomponent, a strong tendency to augment the tore-forming action of theair inlet nozzle means 9, 10, 11. Thus the fuel injection meanscooperates with the primary air injection means in forming the strong,stable tore 8.

The disposition and size of the secondary air inlet ports 12, 13, 14 maytake several forms, but certain fundamental principles must be observed.'It is most important that the initial row of ports 12 should not be soclose to the initial mixing zone as to produce jets which wouldinterfere with the indicated rotation of the smoke ring vortex 8.Specifically, it is believed that this first row of secondary airnozzles should be a minimum distance from the fuel nozzle 5a on theorder of /1. the diameter of the liner, identified D in Fig. 1. It willbe seen from the drawing that this places the nozzles 12 a sufiicientdistance downstream from the tore 8 that there will be little, if any,tendency for the jets from the nozzles 12 to counteract the desireddirection of rotation of the tore. In addition, it is to be noted thatthediameter of theinitial ports "12 is sufficiently small as to producejets long enough to produce adequate mixing with the burning gases, butnot strong enough to produce any significant reverse circulation of thissecondary air to the left into the area occupied by the tore 8. In otherwords, the ports 12 are merely of a size to provide the additional airrequired for the combustion process without having any significanttendency to set up a characteristic flow pattern of their own, or'tointerfere with the flow pattern 8. Specifically, the diameter of thefirst row of holes 12 may be of the liner diameter D.

The second row of inlet ports 13 is spaced somewhat downstream from theports 12, and as shown in the drawing they are approximately at adistance 1 4D from the fuel nozzle. Because of their greater distancefrom the primary mixing and ignition zone, these ports may be of largerdiameter without producing any deleterious effects on the tore 8.Specifically, these ports may be on the order of for example from aboutto the diameter D.

Likewise, the third row of ports 14 may be spaced on the order of 1-%Dfrom the fuel nozzle, and may be on the order of D in diameter.

As shown in Fig. 1, there are six holes in each of the circumferentialrows 12, 13, 14, but it is to be understood that a different number maybe used, specifically the number may range from 6 to perhaps 10. Anormal number would be about 8.

The operation of the combustion chamber shown in Fig. 1 will be fairlyobvious from the above description. A suitable compressor (not shown)supplies air at a pressure which may be on the order of 90 p.s.i.a.through the air supply passage 1:: and to the annular air supply space10. The annular nozzle 9, the vaned nozzles 10,

and the flared entry nozzles 11 produce strong jets of primary air toestablish the tore 8, aided by the kinetic energy of the fuel and airejected from nozzle 5. The strong vortex flow 8 exerts a tearing effecton the surface of the spray pattern 7 tending to break it up andinitiate the mixing and ignition process. The strong vortex 3 retainsthe fuel particles in this initial mixing zone for an interval of timesufficient to initiate combustion. The spark plug or other igniterdevice has been omitted from the drawings because not material to anunderstanding of the present invention. As pri- .mary air continues toenter through the nozzles 9, ll

11, a corresponding amount of hot gasses leave the vortex 8 and progressaxially down the combustion space, as indicated by the arrows 8a. Thesecondary inlets 12 add air in quantities required to keep thecombustion going. The larger nozzles 13 add still more air forcombustion; and the still larger ports 14 admit air in sufiicientquantities to cool the mixture to the temperature desired at the turbineinlet. It will be appreciated that there may be additionalcircumferential rows of ports, of perhaps even larger diameter,downstream from the ports 14, depending on the final temperaturedesired. Ordinarily, itis believed that about three or fourcircumferential rows of secondary inlet ports will be adequate.

It is-also to-be noted that in Fig. l the cooling louvers for providinga film of cooling and insulating air on the inner surfaces of the liner2 have been omitted, for the sake of clarity. It will be understood fromthe Nerad Patent 2,601,000 that it is advisable, if not essential, toprovide the liner wall 2 with any one of many possible patterns oflouvers for admitting a thin film of cooling and insulating air to theinner surface of the liner.

While Fig. 1 illustrates the basic concept and method of operation ofthe invention, the actual mechanical con struction may take many otherforms. Specifically, the end dome 4 of Fig. 1 may be replaced by asomewhat simpler and cheaper end closure, as shown for instance in Fig.2. Here it will be seen that the end closure cornprises a generallyconical member 15 having an inner periphery connected to a reinforcingring-16 engaging the nozzle 5a, and surrounded by a shroud comprising aradially extending annular disk member 17 and'a cylindrical peripheralmember 18. Fig. 3 shows the plan views of the shroud end :disk 17 and ofthe louvered conical member 15. It will be seen that end disk 17 has acircumferential row of inlet ports 17a for admitting air in meteredquantities to the air supply chamber 19. The peripheral cylindricalmember 13 may be supported from the adjacent end of liner 2 by aplurality of spacer members 18a. In turn, the upstream end of liner 2may be supported by a plurality of dowel pins or support struts 20.

The conical member 15 is provided with a central circumferential row ofair inlet ports identified 15a and two circumferential rows of louversidentified 15b, 150. It will be apparent in Fig. 3 that these louversare in staggered arrangement so that each one in the inner row 15boverlaps the gap between adjacent louvers in the outer row 150. It willbe apparent from Fig. 2 how these louvers are stamped from the conicalmember so as to provide a nozzle which projects a jet of air in agenerally radial direction into the combustion space in a directiongenerally tangent to the tore 8. It will be equally obvious how theplain holes 15a provide jets identified 15d in Fig. 2 which perform thefunctions of the jets lilo of Fig. 1. In this connection it will benoted that the air supply ports 17a are so located in the end disk 17 soas nott-o project a strong jet of fluid directly impinging on either thelouvers 15b, 150, or the row of ports 15a. Thus the air entering throughthemetering ports 17a diffuses so as to fill the chamber 19 at asubstantially uniform pressure and random velocity so that there is nostrong velocity of approac to either the ports 15a or the louvers 15b,15c. This provides uniform supply to the jet-producing nozzles so thatthey form stable jets of readily predictable direction.

A significant difference between the fluid flow shown in Fig. 2 and thatof Fig. 1 lies in the fact that the outer cylindrical .end dome member18 is spaced radially from the liner 2 by means of the spacers 18a so asto define a very narrow annular nozzle-projecting a thin annular jet ofcooling and insulating fluid along the inner surface of liner 2, asrepresented by the arrows 13b. It will be seen that, unlike the primaryjets associated with the end closure member, this annular jet 18 doeshave some tendency to counteract the rotation of the tore 8. It shouldbe noted, however, that the annular jet 18b is of very small radialthickness so that the kinetic energy thereof is not great enough toseriously disrupt the toroidal flow 8. It will be seen by comparisonthat the annular nozzle 9 in Fig. 1 provides an annular jet ofsubstantially greater radial thickness. The small flow of cooling andinsulating air indicated by the annular jet 1812 has some slighttendency to cause hot gases rotating in the smoke ring vortex 3 to bepulled away and carried along with the jet lfid, as indicated by thearrow ldc.

As in Fig. 1, the liner of Fig. 2 is provided with a plurality ofcircumferential rows of secondary air inlet ports, identified 12a, 13a,1401. Fig. 2 shows the circumferential row of ports 13%: closer to theinitial row 12a than was the case in Fig. 1. Likewise, the row of ports.14:: is somewhat closer to the fuel nozzle than the row M in Fig. 1.Fig. 2 shows an additional row of still larger ports identified 14b.

The mechanical details of liners and end closure members incorporatingthe invention may obviously take many forms, another of which is shownin Fig. 4. The end closure is generally similar to that shown in Fig. 2having an end disk 17 and a circumferential member 18, with air supplyports 17a and jet-forrning nozzles 15a and louvers 15b, 150. Thedifference is' that the downstream end of member 18 has a flaringportion 18d which cooperates with an adjacent inwardly flaring portion2a of the liner 2, defining an annular clearance space which serves asthe primary nozzle 90, performing the same function as the nozzle 9a ofFig. 1.

Numerous other modifications and substitutions of mechanical equivalentswill occur to those acquainted with the combustor art; and it is ofcourse intended to cover by the appended claims all such modificationsas fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a fluid fuel combustor having a generally cylindrical linerforming the side walls of an elongated combustion space with an opendischarge end, an end closure member defining the fuel inlet end of thecombustion space, and Walls surrounding and spaced from the liner toform passages for supplying combustion air uniformly under pressure tothe combustion space, the combination of fuel injection means disposedto spray fuel particles into the primary mixing and ignition zoneadjacent the end closure with a high velocity spray pattern in the formof a cone having a vertex angle not exceeding about 60 and with its axisgenerally coincident with the axis of the liner, primary nozzle meanscomprising directed jet-forming air metering means disposed on the wallof said end closure forming varying angles of incidence with the lineraxis and disposed to receive air from said supply passages and toproject strong primary jets of air into said mixing zone in a directiongenerally tangent to a double-opposed-toroidal flow path created by saidprimary jets and substantially filling the primary mixing zone adjacentthe end closure member, said toroidal flow being also generally tangentto and in the same general direction as said conical fuel spray patternwhereby the velocity energy of the fuel spray augments the toreformingaction of said primary nozzle means, and secondary nozzle means in theliner wall for injecting additional secondary air to support thecombustion process in a secondary zone downstream from the primarymixing zone, said secondary nozzle means being disposed at a transverseplane located a distance at least equal to /1 of the liner diameter Ddownstream from the fuel nozzle means, said secondary nozzle meansproducing jets of a size and direction to insure good mixing ofsecondary air with the burning fuel in said secondary zone butsubstantially without tending to quench the flame in the primary mixingand ignition zone and substantially without impinging upon saiddouble-opposedtoroidal flow in the primary mixing zone.

2. A fluid-fuel eombustor in accordance with claim 1 having additionalsecondary jet producing means comprising a circumferential row of on theorder of eight secondary air inlet ports equally spaced around the linerand being of a diameter on the order of the liner diameter D, saidcircumferential row of secondary ports being spaced on the order of 1%Dfrom the inlet end of the combustion space.

3. A fluid fuel combustor in accordance with claim 2 and including thirdsecondary air jet means comprising an additional circumferential row ofair inlet openings each being on the order of D in diameter and spacedon the order of 1%D from the inlet end of the combustion space.

' closure member defining the fuel inlet end of the combustion space,and walls surrounding and spaced from the liner to form passages forsupplying combustion air under pressure to the combustion space, thecombination of fuel injection means disposed to spray fuel particlesinto the primary mixing and ignition zone adjacent the end dome with ahigh velocity fuel spray pattern in the form of a cone having a vertexangle not exceeding 60 and with its axis substantially coincident withthe axis of the liner, primary nozzle means comprising directedjet-forming air metering means disposed on the wall of said end domeforming varying angles of incidence with the liner axis and disposed toreceive air from said supply passages and to produce strong primary jetsof air into said mixing zone in directions generally tangent to adouble-opposed-to-roidal flow created by said jets and substantiallyfilling said primary mixing zone, said toroidal flow being alsogenerally tangent to and in the same general direction as said conicalfuel spray pattern whereby the velocity energy of the fuel sprayaugments the tore-forming action of said primary air jets, and secondarynozzle means in the liner wall for injecting additional secondary air tosupport the combustion process in a secondary zone downstream from theprimary zone, said secondary nozzle means including a firstcircumferential row of on the order of eight equally spaced secondaryair inlet ports disposed at a common transverse plane located at adistance on the order of 3X4 of the liner diameter D downstream from thefuel nozzle means, each of said first row of secondary ports being of ,adiameter on the order of D and disposed to project a jet of air into thecombustion space in a direction to insure good mixing with the burningfuel in said secondary zone but substantially without tending to quenchthe flame, and at least a second circumferential row of secondary airinlet ports in said liner wall and located downstream from and being ofa larger diameter than said first row of secondary ports, wherebysecondary combustion air and cooling and dilution air are admitted tothe combustion space in progressively larger quantities in the secondaryzone as the burning fuel passes toward the open end of the liner,without impinging upon the toroidal flow in the primary mixing zone.

References Cited in the file of this patent UNITED STATES PATENTS1,474,867 Walker Nov. 20, 1923 2,143,259 Clarkson Jan. 10, 19392,555,965 Garber June 5, 1951 2,595,999 Way et al May 6, 1952 2,601,000Nerad June 17, 1952 2,621,477 Powter et al Dec. 16, 1952 2,651,912Abbott Sept. 15, 1953 2,699,648 Berkey Jan. 18, 1955 FOREIGN PATENTS840,943 France Jan. 28, 1939

